Page:Popular Science Monthly Volume 74.djvu/234

present in other portions of the leaf. The result was recorded by exposing the leaf to sunlight in contact with the velox paper in a printing frame. The region lacking starch, being more translucent, gave the darkest image on the velox paper (Fig. 10).

It was found possible to increase the rate of respiration of germinating seeds by means of the rays, and alcoholic fermentation was also accelerated by suitable exposure, as follows: Five fermentation tubes

Fig. 10.

were filled with equal quantities of a mixture of 2 gm. of a compressed yeast cake in 250 c.c. of a 5 per cent, solution of cane-sugar. Into four of the fermentation tubes were placed sealed glass tubes as follows: RaBr2 1,500,000 X; 10,000 X; 7,000 X; radio-tellurium. The fifth served as a control. At the end of about three and one half hours the cultures were photographed (Fig. 11). It is clearly shown in the figure that the rate of alcoholic fermentation, as measured by the evolution of gas, was accelerated by the rays; most by the preparation of 1,500,000 activity, least by that of 7,000 activity, and to an intermediate degree by the other preparations.

Various attempts have been made to detect a tropistic response, or curvature of a growing organ toward or from a radioactive source. The phosphorescent light of radium has not been found intense enough to call forth phototropic curvatures, and the existence of a true radiotropism is yet to be demonstrated. Koernicke found that seedlings